The present invention relates generally to a hermetic scroll-type compressor and, more particularly, to such a compressor having fixed and orbiting scroll members, wherein a compliance mechanism acts on the orbiting scroll plate to bias it axially and radially toward the fixed scroll member for proper mating and sealing therebetween.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
It is generally believed that the scroll-type compressor could potentially offer quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design problems persist that have prevented the scroll compressor from achieving wide market acceptance and commercial success. For instance, during compressor operation, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the opposite scroll member. Such leakage causes reduced compressor operating efficiency and, in extreme cases, can result in an inability of the compressor to operate.
Leakage between compression pockets of a scroll compressor may also occur at those locations where the wrap walls sealingly contact each other to define the moving compression pockets. Specifically, the pressure of the compressed refrigerant in the compression pockets, together with manufacturing tolerances of the component parts, may cause slight radial separation of the scroll members and result in the aforementioned leakage.
Efforts to counteract the separating forces applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakages, have resulted in the development of several prior art compliance schemes. With respect to axial compliance mechanisms, it is known to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. However, this approach results in high initial frictional forces between the scroll members and/or bearings when the compressor is at rest, thereby causing difficulty during compressor startup. Another prior art approach involves assuring close manufacturing tolerances for component parts and having the separating force borne by a thrust bearing. This approach not only requires an expensive thrust bearing, but also involves high manufacturing costs in maintaining close machining tolerances.
A number of prior art patents disclose a scroll-type compressor design in which an intermediate pressure chamber is provided behind the orbiting scroll member, whereby the intermediate pressure creates an upward force to oppose the separating force. Such a design recognizes the fact that suction pressure behind the orbiting scroll member is insufficient to oppose the separating force, while discharge pressure behind the orbiting scroll member results in too great an upward force causing rapid wear of the scroll wraps and faces. However, establishing an intermediate pressure between suction pressure and discharge pressure requires that an intentional leak be introduced between an intermediate pressure pocket and a discharge pressure region. Such a leak results in less efficient operating conditions for the compressor.
Several other prior art scroll compressor designs, directed to controlling the upward force on the orbiting scroll member to oppose the separating force, have utilized a combination of gaseous refrigerant at suction pressure and gaseous refrigerant at discharge pressure for exposure to respective areas on the backside of the orbiting scroll member. In such compressor designs, various seal means have been utilized to separate the respective gaseous pressure regions. For instance, it is known to utilize an annular seal element intermediate the bottom surface of the orbiting scroll member and an adjacent fixed frame member, whereby the seal element extends toward and slidingly seals against the bottom surface. A problem with such a seal arrangement is that the relative orbiting motion of the scroll member with respect to the seal element changes the axial force distribution on the scroll member, thereby generating an unwanted moment. Also the seal may undergo additional wear if it has to support sealing functions in the axial and radial directions at the same time.
Another axial compliance mechanism for a scroll compressor involves respective regions of the orbiting scroll member bottom surface exposed to oil at discharge pressure and refrigerant fluid at suction pressure. The regions are sealingly separated by a flexible annular seal element that is disposed between the orbiting scroll member bottom surface and a rotating thrust surface comprising a radially extending plate portion of a drive crankshaft.
Radial compliance of the scroll members toward one another, whereby sealing between respective wrap walls is promoted, has typically been accomplished by a swing-link drive mechanism that couples the orbiting scroll member to the drive shaft. While satisfactory results have been achieved with such a mechanism, substitution of a radial compliance mechanism not associated with the drive function would simplify the compressor design, thereby improving manufacturability.
Another method of practicing radial compliance involves a two-piece orbiting scroll design, wherein a separate wrap member is loosely connected to a plate member, thereby allowing the wrap to move slightly in the radial direction. A problem with this design is that a sliding interface between the base of the wrap member and the surface of the plate member is a potential location for leakage between compression pockets.
The present invention is directed to overcoming the aforementioned problems associated with scroll-type compressors, wherein it is desired to provide both axial and radial forces on the orbiting scroll member to facilitate sealing and prevent leakage between the interfitting scroll members.